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Wed, 29 Apr 2020 19:20:09 +0000 Subject: Re: [PATCH bpf-next v1 07/19] bpf: create anonymous bpf iterator To: Martin KaFai Lau , Andrii Nakryiko CC: Andrii Nakryiko , bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team References: <20200427201235.2994549-1-yhs@fb.com> <20200427201242.2995160-1-yhs@fb.com> <2b88797e-23b3-5df0-4d06-00b26912d14a@fb.com> <20200429184623.ul7nxelzxeip2ign@kafai-mbp> From: Yonghong Song Message-ID: <88bfc829-3c2d-96aa-7d32-4f3ff9b4ad08@fb.com> Date: Wed, 29 Apr 2020 12:20:05 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 In-Reply-To: <20200429184623.ul7nxelzxeip2ign@kafai-mbp> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: CO1PR15CA0089.namprd15.prod.outlook.com (2603:10b6:101:20::33) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from macbook-pro-52.local.dhcp.thefacebook.com (2620:10d:c090:400::5:99f7) by CO1PR15CA0089.namprd15.prod.outlook.com (2603:10b6:101:20::33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2937.13 via Frontend Transport; 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When fops->release() is called, just based on >>>>> inode and file, bpf program cannot be located since target >>>>> seq_priv_size not available. This map helps retrieve the prog >>>>> whose reference count needs to be decremented. >>>>> >>>>> Signed-off-by: Yonghong Song >>>>> --- >>>>> include/linux/bpf.h | 3 + >>>>> include/uapi/linux/bpf.h | 6 ++ >>>>> kernel/bpf/bpf_iter.c | 162 ++++++++++++++++++++++++++++++++- >>>>> kernel/bpf/syscall.c | 27 ++++++ >>>>> tools/include/uapi/linux/bpf.h | 6 ++ >>>>> 5 files changed, 203 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h >>>>> index 4fc39d9b5cd0..0f0cafc65a04 100644 >>>>> --- a/include/linux/bpf.h >>>>> +++ b/include/linux/bpf.h >>>>> @@ -1112,6 +1112,8 @@ struct bpf_link *bpf_link_get_from_fd(u32 ufd); >>>>> int bpf_obj_pin_user(u32 ufd, const char __user *pathname); >>>>> int bpf_obj_get_user(const char __user *pathname, int flags); >>>>> >>>>> +#define BPF_DUMP_SEQ_NET_PRIVATE BIT(0) >>>>> + >>>>> struct bpf_iter_reg { >>>>> const char *target; >>>>> const char *target_func_name; >>>>> @@ -1133,6 +1135,7 @@ int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx); >>>>> int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog); >>>>> int bpf_iter_link_replace(struct bpf_link *link, struct bpf_prog *old_prog, >>>>> struct bpf_prog *new_prog); >>>>> +int bpf_iter_new_fd(struct bpf_link *link); >>>>> >>>>> int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value); >>>>> int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value); >>>>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h >>>>> index f39b9fec37ab..576651110d16 100644 >>>>> --- a/include/uapi/linux/bpf.h >>>>> +++ b/include/uapi/linux/bpf.h >>>>> @@ -113,6 +113,7 @@ enum bpf_cmd { >>>>> BPF_MAP_DELETE_BATCH, >>>>> BPF_LINK_CREATE, >>>>> BPF_LINK_UPDATE, >>>>> + BPF_ITER_CREATE, >>>>> }; >>>>> >>>>> enum bpf_map_type { >>>>> @@ -590,6 +591,11 @@ union bpf_attr { >>>>> __u32 old_prog_fd; >>>>> } link_update; >>>>> >>>>> + struct { /* struct used by BPF_ITER_CREATE command */ >>>>> + __u32 link_fd; >>>>> + __u32 flags; >>>>> + } iter_create; >>>>> + >>>>> } __attribute__((aligned(8))); >>>>> >>>>> /* The description below is an attempt at providing documentation to eBPF >>>>> diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c >>>>> index fc1ce5ee5c3f..1f4e778d1814 100644 >>>>> --- a/kernel/bpf/bpf_iter.c >>>>> +++ b/kernel/bpf/bpf_iter.c >>>>> @@ -2,6 +2,7 @@ >>>>> /* Copyright (c) 2020 Facebook */ >>>>> >>>>> #include >>>>> +#include >>>>> #include >>>>> #include >>>>> >>>>> @@ -19,6 +20,19 @@ struct bpf_iter_link { >>>>> struct bpf_iter_target_info *tinfo; >>>>> }; >>>>> >>>>> +struct extra_priv_data { >>>>> + struct bpf_prog *prog; >>>>> + u64 session_id; >>>>> + u64 seq_num; >>>>> + bool has_last; >>>>> +}; >>>>> + >>>>> +struct anon_file_prog_assoc { >>>>> + struct list_head list; >>>>> + struct file *file; >>>>> + struct bpf_prog *prog; >>>>> +}; >>>>> + >>>>> static struct list_head targets; >>>>> static struct mutex targets_mutex; >>>>> static bool bpf_iter_inited = false; >>>>> @@ -26,6 +40,50 @@ static bool bpf_iter_inited = false; >>>>> /* protect bpf_iter_link.link->prog upddate */ >>>>> static struct mutex bpf_iter_mutex; >>>>> >>>>> +/* Since at anon seq_file release function, the prog cannot >>>>> + * be retrieved since target seq_priv_size is not available. >>>>> + * Keep a list of mapping, so that >>>>> + * at file release stage, the prog can be released properly. >>>>> + */ >>>>> +static struct list_head anon_iter_info; >>>>> +static struct mutex anon_iter_info_mutex; >>>>> + >>>>> +/* incremented on every opened seq_file */ >>>>> +static atomic64_t session_id; >>>>> + >>>>> +static u32 get_total_priv_dsize(u32 old_size) >>>>> +{ >>>>> + return roundup(old_size, 8) + sizeof(struct extra_priv_data); >>>>> +} >>>>> + >>>>> +static void *get_extra_priv_dptr(void *old_ptr, u32 old_size) >>>>> +{ >>>>> + return old_ptr + roundup(old_size, 8); >>>>> +} >>>>> + >>>>> +static int anon_iter_release(struct inode *inode, struct file *file) >>>>> +{ >>>>> + struct anon_file_prog_assoc *finfo; >>>>> + >>>>> + mutex_lock(&anon_iter_info_mutex); >>>>> + list_for_each_entry(finfo, &anon_iter_info, list) { >>>>> + if (finfo->file == file) { >>>> >>>> I'll look at this and other patches more thoroughly tomorrow with >>>> clear head, but this iteration to find anon_file_prog_assoc is really >>>> unfortunate. >>>> >>>> I think the problem is that you are allowing seq_file infrastructure >>>> to call directly into target implementation of seq_operations without >>>> intercepting them. If you change that and put whatever extra info is >>>> necessary into seq_file->private in front of target's private state, >>>> then you shouldn't need this, right? >>> >>> Yes. This is true. The idea is to minimize the target change. >>> But maybe this is not a good goal by itself. >>> >>> You are right, if I intercept all seq_ops(), I do not need the >>> above change, I can tailor seq_file private_data right before >>> calling target one and restore after the target call. >>> >>> Originally I only have one interception, show(), now I have >>> stop() too to call bpf at the end of iteration. Maybe I can >>> interpret all four, I think. This way, I can also get ride >>> of target feature. >> >> If the main goal is to minimize target changes and make them exactly >> seq_operations implementation, then one easier way to get easy access >> to our own metadata in seq_file->private is to set it to point >> **after** our metadata, but before target's metadata. Roughly in >> pseudo code: >> >> struct bpf_iter_seq_file_meta {} __attribute((aligned(8))); >> >> void *meta = kmalloc(sizeof(struct bpf_iter_seq_file_meta) + >> target_private_size); >> seq_file->private = meta + sizeof(struct bpf_iter_seq_file_meta); > I have suggested the same thing earlier. Good to know that we think alike ;) > > May be put them in a struct such that container_of...etc can be used: > struct bpf_iter_private { > struct extra_priv_data iter_private; > u8 target_private[] __aligned(8); > }; This should work, but need to intercept all seq_ops() operations because target expects private data is `target_private` only. Let me experiment what is the best way to do this. > >> >> >> Then to recover bpf_iter_Seq_file_meta: >> >> struct bpf_iter_seq_file_meta *meta = seq_file->private - sizeof(*meta); >> >> /* voila! */ >> >> This doesn't have a benefit of making targets simpler, but will >> require no changes to them at all. Plus less indirect calls, so less >> performance penalty. >>